http://www.bouncycastle.org/java.html: The Bouncy Castle Java APIs for CMS, PKCS, EAC, TSP, CMP, CRMF, OCSP, and certificate generation. This jar contains APIs for JDK 1.5 to JDK 1.8. The APIs can be used in conjunction with a JCE/JCA provider such as the one provided with the Bouncy Castle Cryptography APIs.
  • The Legion of the Bouncy Castle Inc. 
package org.bouncycastle.operator;

import java.io.OutputStream;

import org.bouncycastle.asn1.x509.AlgorithmIdentifier;


General interface for a key initialized operator that is able to calculate a MAC from
a stream of output.

/**
 * General interface for a key initialized operator that is able to calculate a MAC from
 * a stream of output.
 */
public interface MacCalculator
{
    AlgorithmIdentifier getAlgorithmIdentifier();

    
Returns a stream that will accept data for the purpose of calculating
the MAC for later verification. Use org.bouncycastle.util.io.TeeOutputStream if you want to accumulate
the data on the fly as well.

Returns:an OutputStream
/**
     * Returns a stream that will accept data for the purpose of calculating
     * the MAC for later verification. Use org.bouncycastle.util.io.TeeOutputStream if you want to accumulate
     * the data on the fly as well.
     *
     * @return an OutputStream
     */
    OutputStream getOutputStream();

    
Return the calculated MAC based on what has been written to the stream.

Returns:calculated MAC.
/**
     * Return the calculated MAC based on what has been written to the stream.
     *
     * @return calculated MAC.
     */
    byte[] getMac();


    
Return the key used for calculating the MAC.

Returns:the MAC key.
/**
     * Return the key used for calculating the MAC.
     *
     * @return the MAC key.
     */
    GenericKey getKey();
}